This section provides background information related to the present disclosure which is not necessarily prior art.
In automotive vehicles, it is common to have a climate control system located within an instrument panel which provides heated or cooled air to occupants through dash panel defrost air outlets, instrument panel venting air outlets and floor directed air outlets. These traditional climate control systems often include a heater core that performs heat exchange between the engine coolant, which is heated by the engine, and the cool air in the cabin/outside environment, in order to provide warm air to the passenger compartment. Some vehicles include an air conditioning system that incorporates an evaporator for absorbing heat from the warm air in the cabin and from the outside environment. The heater core and evaporator are typically provided in an HVAC housing located in the passenger compartment of the vehicle. The evaporator and heater core are generally disposed downstream of a fan for communicating cooled or warmed air into the passenger compartment.
A fresh air/recirculation air switching case is also used in a vehicle climate control system for switching and introducing an outside air and an inside air into the fan then through the desired heat exchangers and ultimately to the passenger cabin of the vehicle. To control the amount of fresh outside air or recirculation air, a rotary door having an arc-shaped circumferential wall is disposed inside the case. The rotary door opens and closes an inside air introduction inlet and an outside air introduction inlet. In the fresh air/recirculation air switching case employing a rotary door creates a packaging advantage because the door installation space can be reduced as compared with an ordinary flat plate door.
However, according to the present inventors' experiments and evaluations, the inside fresh air/recirculation air switching case using a rotary door may create a problem that air flow noise increases and become objectionable to passengers in the vehicle. This noise is created by the introduced air flowing from one end to the other end of the circumferential wall of the rotary door along the inner surface thereof. As a result, the flow of the air creates a turbulent pocket underneath the circumferential wall of the rotary door which causes unwanted noise to enter in the passenger cabin of the vehicle.
U.S. Pat. No. 5,836,813 provided several ways to address this particular issue. This patent disclosed using a guide attached to the inside of the circumferential wall; this guide will direct the air flow and prevent turbulence. Additionally, this patent disclosed using a reflection plate, for irregularly reflecting the noise, this plate protrudes from the inner surface of the circumferential wall of the rotary door. However, neither embodiment fully eliminates the potential for turbulent flow from occurring under the circumferential wall.
U.S. Pat. No. 7,575,511 provides including a convex surface under the circumferential wall, however this patent discloses one solid surface. It is understood in the art that having an integrally molded rotary door with 2 curved opposite surfaces is extremely difficult to manufacture and control quality of the component itself. Additionally, adding the convex surface as a second piece to the rotary door complicates manufacturing and may reduce production efficiency.
It would be desirable to automotive HVAC system which provides an easily manufactured fresh air/recirculation air switching door that eliminates potential for turbulent air flow to occur under the circumferential wall and lead to unwanted noise in the vehicle cabin.